Isotropic deposition for trench narrowing of features to be created by reactive ion etch processing

ABSTRACT

An isotropic deposition method for trench narrowing of thin film magnetic write head features to be created by reactive ion etching. According to the method, a photolithographically defined photoresist trench is formed over a hardmask and underlying polymer layer as part of tri-layer resist process. Instead of performing the usual hardmask and polymer etching steps using the photoresist mask pattern, a spacer layer is deposited isotropically or directionally at an angle to cover the vertical side walls of the trench. The spacer layer is etchable by the hardmask etch process but resistant to the polymer etch process. When the hardmask etch process is performed, the spacer layer material applied to the trench side walls remains intact, thereby defining a narrowed trench that is extended by the subsequent base layer etch process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thin film heads for magneticallywriting information on data storage media, and particularly tofabrication processes for manufacturing such heads. Still moreparticularly, the invention concerns the reduction of write head featuresize beyond that which can be achieved using conventionalphotolithography.

2. Description of the Prior Art

By way of background, thin film magnetic write heads for use in datastorage devices, such as disk drives, conventionally include featuressuch as P1 and P2 pole pieces that cooperate to record magnetic domainsin concentric track patterns on an underlying data storage medium. Theconfiguration of the pole pieces, and particularly the track widthfeature size, is an important determinant of the track width of themagnetic domains recorded on the underlying medium. Because narrow trackwidth translates to increased data storage capacity, all other thingsbeing equal, it is a design goal of disk drive manufacturers to reducethe track width feature size of the pole pieces.

In thin film magnetic head processing, features are constructed usingphotolithographic processes. For example, to fabricate a pole piece, aphotoresist layer is formed, then photo-exposed using aphotolithographic mask to define the pole piece geometry, and thenphoto-developed to form a trench conforming to the defined geometry. Themetallic pole piece material (typically a nickel-iron alloy) isdeposited in the trench using an electroplating process. The remainingphotoresist material is then stripped away, leaving behind the fullyformed pole piece. In a tri-layer resist process, a feature is formed ina polymer layer using a “hardmask” layer over the polymer material. Astandard photoresist layer is spun onto the hardmask and patterned todefine the desired etch mask. Two etching processes are used to firstetch the hardmask and then the polymer layer. The function of the hardmask is to ensure that the feature is formed anisotropically in thepolymer layer during the second etching phase.

The problem with this type of processing is that feature size can onlybe narrowed photolithographically by using shorter wavelength light andcontrast enhancement techniques. Thus, whether conventionalphotolithography is used, or newer technologies such as deep UV orelectron beam lithography, reductions in feature size typically requirenew and more expensive light sources and exposure technology. Anadditional disadvantage of photolithographic solutions is that line edgeroughness becomes a concern as photolithographic features become eversmaller.

Accordingly, an improved technique for reducing feature size in a thinfilm magnetic write head is required if improvements in disk driveperformance are to be achieved. What is particularly needed is a newtechnique whereby feature size can be reduced while using any thin filmmagnetic head photolithographic process, including deep UV or electronbeam lithography, without having to invest in higher costphotolithographic resolution enhancement solutions. An additionaldesirable requirement is that the technique be compatible with atri-layer resist process in which a hardmask and an underlying polymerlayer are separately etched to define features. A further requirement isthat of reducing the line edge roughness of the photolithographicallydefined trenches.

SUMMARY OF THE INVENTION

The foregoing problems are solved and an advance in the art is obtainedby a novel isotropic deposition method for trench narrowing of thin filmmagnetic write head features to be created by reactive ion etching.According to the method, a polymer base layer is formed on a substrate,such as an electroplating seed layer. A hardmask layer (hardmask) isapplied onto the polymer layer and a photoresist imaging layer is spunonto the hardmask to a desired thickness. A trench is defined in thephotoresist layer to form a pattern for the feature. The trench is deepenough to expose the hardmask, and has substantially vertical sidewalls. Following formation of the trench, a spacer layer is depositedisotropically or directionally at an angle to cover the trench sidewalls. The material used to form the spacer layer is one that can bedeposited isotropically while preserving trench geometry, ordirectionally at an angle. The material must also be etchable by asubsequent hardmask etch process and resistant to a subsequent baselayer etch process.

Horizontal portions of the spacer layer that overlie the bottom of thetrench (if any) are anisotropically etched as part of the hardmask etchprocess to remove such material. Hardmask material is also removed fromthe trench bottom to expose the polymer layer. Vertical portions of thespacer layer that cover the trench side walls are left intact. Thisprocess initiates the formation of a narrowed trench that is reduced inhorizontal size according to approximately twice the thickness of thespacer layer as deposited on the trench side walls.

The base layer etch process extends the trench anisotropically throughthe polymer layer to reveal the underlying substrate. This is donewithout removing the spacer layer material from the trench sidewalls, sothat the narrowed trench size is carried through the polymer to thesubstrate. A feature, such as a metallic pole piece, may now be formedby electroplating metallic material into the narrowed trench.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other features and advantages of the invention will beapparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingDrawing, in which:

FIG. 1 is a simplified vertical sectional view of a magnetic disk drivethat incorporates a magnetic write head made according the presentinvention;

FIG. 2 is a simplified horizontal sectional view of the disk drive ofFIG. 1;

FIG. 3 is a sectional view taken through the track width centerline ofan integrated magnetic read/write head made in accordance with theinvention;

FIG. 4 is a front elevational view (taken from the air bearing surface)of the integrated read/write head of FIG. 3; and

FIGS. 5A-5E are a sequence of diagrammatic sectional views showing theformation of a write head with reduced feature size according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to the figures, wherein like reference numerals representlike elements in all of the several views, FIGS. 1 and 2 illustrate adisk drive 2 that includes a magnetic write head constructed using themethod of the invention. The disk drive 2 conventionally includes a basecasting 4 made from aluminum or other suitable material. A cover 5 isremovably mounted thereto via a hermetic seal (not shown). The basecasting 4 supports a conventional spindle drive motor 6 having anassociated drive spindle 8. The drive spindle 8 carries a disk 10 forhigh speed rotation therewith. Other disks (not shown) may also becarried on the drive spindle 8 to form a spaced vertically stacked diskplatter arrangement. The disk 10 is made from a suitable material of atype usually found in magnetic disk drive assemblies. In particular, thedisk 10 is formed from an aluminum or glass substrate with appropriatecoatings being applied thereto such that at least one, and preferablyboth, of the upper and lower surfaces of the disk are magneticallyencodable and aerodynamically configured for high speed interaction witha read/write transducer (described below).

Data access to the disk 10 is achieved with the aid of an actuator 12that is mounted for rotation about a stationary pivot shaft 14. Theactuator 12 includes a rigid actuator arm 16 that carries a flexiblesuspension 18. The suspension 18 in turn carries a slider 20 that mountsa transducer 22. The transducer 22 is an integrated device that includesa magnetic write head and a read head that may incorporate aconventional magnetoresistive sensor or the like. The actuator 12, whichis conventionally driven by a voice coil motor 24, moves the slider 20generally radially across the surface of the disk 10 so that thetransducer 22 is able to trace concentric data tracks on the disk.

Data is recorded on the disk 10 by the write head portion of thetransducer 22. Data is read from the disk 10 by the read head portion ofthe transducer 22. This data is processed into a readback signal bysignal amplification and processing circuitry (not shown) that isconventionally located on the actuator arm 16. The readback signal,which carries both data and transducer position control information, issent to the drive controller 25 for conventional processing. Thecontroller 25 also generates write data and position control informationduring data write operations.

It will be appreciated that the foregoing detailed description of thedisk drive 2 and the transducer 22 is exemplary in nature, and that manyother design configurations would be possible while still incorporatinga write head that has been fabricated according to the invention. Forexample, the disk drive 2 may include a large number of disks andactuators, and each actuator may carry plural suspensions and multiplesliders. Moreover, instead of using an air bearing slider, analternative transducer carrying structure may be used that maintains thetransducer 22 in contact or near contact with the disk 10.

Turning now to FIGS. 3 and 4, the write head portion of the transducer22 is shown at 26 and the read head portion of the transducer is shownat 28. The transducer 22 is shown in FIG. 3 as being lapped at 29 toform an air bearing surface (ABS). This ABS 29 is spaced from therotating disk 10 during drive operation by virtue of the above-describedair bearing. FIG. 4 shows the transducer 22 from the vantage point ofthe ABS 29.

The write head 26 conventionally includes a combined layer comprising 12insulative material 30 and plural inductive coil loops 32. The combinedinsulation and coil layer 30/32 is formed on an I1 insulation layer 34.The coils of the combined layer 30/32 inductively drive first and secondpole pieces 36 and 38. A G3 gap layer 40 is sandwiched between the polepieces 36 and 38 to provide a magnetic write gap at the pole tips 36 aand 38 a located adjacent to the ABS 29. Note that the pole piece 36 iscommonly referred to as a “P1” pole piece and is labeled as such in FIG.3. The pole piece 38 may either be referred to as a “P2” or “P3” polepiece depending on how the pole tip 38 a is formed. If, as shown in FIG.3, the pole tip 38 a is formed separately from the pole piece 38, thepole piece 38 is referred to as a “P3” pole piece (and is labeled assuch in FIG. 3) and the pole tip 38 a is referred to as a “P2 stub” (asalso shown in FIG. 3). If the pole tip 38 a is formed with as part ofthe pole piece 38, the pole piece 38 is referred to as a “P2” polepiece. During a data write operation, signal current is conductedthrough the coils C of the combined layer 30/32, and flux is inducedinto the pole pieces 36 and 38. This flux fringes across the pole tips36 a and 38 a at the ABS 29 and forms magnetic domains on the rotatingdisk 10. As indicated above, the magnetic domains are arranged to defineconcentric tracks on the disk 10. Note that the back gap portion of thewrite head 26 is not shown in FIG. 3.

FIG. 4 shows the face of the pole tip portions 36 a and 38 a of the polepieces 36 and 38. The track width feature size of the pole tips 36 a and38 a is defined by the dimension TW in FIG. 4. It will be seen that thepole piece 36 also includes a lower portion that extends beyond thetrack width dimension TW. This configuration is shown by way of exampleonly and will not necessarily be found in other write heads made inaccordance with the invention.

The read head 28 of FIGS. 3 and 4 includes a thin film read sensor 42disposed in adjacent G1 and G2 gap areas 44 and 46. The G1 and G2 gapareas 44 and 46 are in turn sandwiched between a first (S1) magneticshield layer 48 and second (S2) magnetic shield layer 50 that in somedesigns may also be used to provide the pole piece 36. The S1 shieldlayer 48 is conventionally formed over the slider 20, which is onlypartially shown in FIGS. 3 and 4 for clarity. During a read operation,magnetized domains on the concentric tracks of the rotating disk 10inject flux into the read sensor 42. This influences the read sensor 42,causing a corresponding signal to be produced by the read sensor'ssensing circuit (not shown).

Turning now to FIGS. 5A-5E, a method is shown for producing features ofthe write head 26, such as the pole piece 38, so that its pole tip 38 ahas reduced track width feature size at the ABS 29. Each of FIGS. 5A-5Eis a sectional view taken along what will become the ABS 29 of thetransducer 22, such that the pole piece track width feature size can beillustrated.

In FIG. 5A, a plating seed layer 60 comprising a nickel-iron (NiFe)alloy, a nickel-iron-cobalt (NiFeCo) alloy, an iron-aluminum alloy(FeAl) or any other suitable seed layer metal, is applied over anunderlying structure (not shown) to a thickness of about 0.1 μm. Afterformation of the seed layer 60, which serves as a substrate for thesubsequent layers, a base layer 62 is applied over the seed layer to athickness of about 3-5 μm. The base layer 62 can be made from anysuitable polymer, including Novalac resin, available under the productdesignation RMPN-60 from Sumitomo Chemical Co., Inc. A hardmask layer64, made from tantalum oxide or the like, is applied over the base layer62 to a thickness of about 0.1 μm. A photoresist imaging layer 66comprising a conventional photoactive polymer material is spun onto thehardmask 64 to a thickness of about 0.5 μm.

In FIG. 5B, a trench 68 is defined in the photoresist layer 66 toinitiate the formation of a stencil for the feature of interest. Thetrench 68 is defined using the usual photoresist masking techniques,with the photoresist material being either a negative resist, or moreconventionally, a positive resist. Using a wet etching process to removethe exposed photoresist material, the trench 68 will extend to thehardmask 64, and will be defined by a trench bottom 70 and substantiallyvertical side walls 71 that extend from the trench bottom to the top ofthe photoresist layer 66.

As shown in FIGS. 5C-1 and 5C-2, following formation of theresist-imaged trench 68 of FIG. 5B, a spacer layer 72 is deposited tocover at least the trench side walls 71. Preferred deposition techniquesinclude isotropic deposition using a process such as PVD (Physical VaporDeposition), CVD (Chemical Vapor Deposition) including PECVD (PlasmaEnhanced CVD), or IBD (Ion Beam Deposition). FIG. 5C-1 illustrates anisotropically deposited spacer layer 72 that covers not only the trenchvertical side walls 71, but also the trench bottom 70.

Note that the deposition process should preferably be one that can beimplemented at relatively low temperature, e.g., less than about 100°Celsius, so that there is no softening of the photoresist layer 66. Thisrequirement may be relaxed if a photoresist material is used which iscompatible with higher temperatures. However, the temperature must notbe so high as to cause degradation of the material layers of the readsensor 42.

As an alternative to isotropic deposition, the spacer layer 72 can beapplied directionally at an angle using angled IBD or ion-assisted IBD(both of which are low temperature processes). According to thistechnique, and as illustrated in FIG. 5C-2, the spacer layer material isapplied at an angle of between 0-90° (relative to the vertical axis ofthe trench 68) to coat the trench side walls 71 while minimizing oreliminating the deposition of spacer layer material at the trench bottom70. This can help compensate for lag during subsequent RIE (Reactive IonEtching) of the hardmask layer 64 and the polymer layer 62. Thetechnique can be practiced both with substrate rotation and with a fixedrotation angle perpendicular to the trench 68.

The material used to form the spacer layer 72 must be carefully selectedaccording to several criteria. In particular, the spacer layer materialmust be (1) capable of being deposited isotropically while faithfullypreserving the shape of the trench 68, or directionally at an angle, (2)etchable in a subsequent hardmask etch, and (3) resistant to asubsequent base layer etch. The latter requirement ensures that thespacer layer material will help preserve the hardmask etch dimensionduring polymer etching. Materials that can satisfy all of the foregoingrequirements are elements, compounds or alloys that can be easilydeposited using one of the deposition processes described above andwhich can also be easily removed in an anisotropic manner by reactiveion etch methods using halogen or halogen compound etchants andimplemented at relatively low temperatures (i.e., less than 100°Celsius) in order to avoid deformation of the trench-defining resistfeatures.

Candidate elements having the potential to satisfy all of the foregoingrequirements are metals and semiconductors, including carbon, in Groups1b, 2b, 3a/b, 4a/b, 5a/b, 6b, 7b and 8 of the Periodic Table ofElements. Oxides, nitrides and carbides of such materials, as well asother compounds and alloys containing such materials, may also be used,as can combinations of any of the foregoing. If multiple spacer layermaterials are used, they may be applied in multiple spacer sub-layersuntil the full spacer layer 72 is formed.

By way of example only and not by way of limitation, exemplary elementalmaterials that may be used to form the spacer layer 72 include silicon,germanium, tungsten, tantalum and titanium. Exemplary compounds includeoxides, nitrides and carbides of silicon, germanium, tungsten, tantalumand titanium. Exemplary alloys include SiGe, GaAs, and others.

As indicated, the formation of the spacer layer 72 can be performed inmultiple stages using different materials. In one particularlyadvantageous construction, the spacer layer 72 may be formed by firstapplying a coating of tantalum or titanium (or other suitable material)and then applying a coating of tungsten. Tungsten is advantageousbecause it facilitates focused ion beam imaging of a small area of aproduction thin film wafer for periodic process control monitoring orother testing. It is also more readily etchable by the hardmask etchprocess now to be discussed. A disadvantage of tungsten is that it mustbe applied at relatively high temperature, which, if not for theundercoating of tantalum or titanium (or other material), could causeundesirable widening/flaring of the trench 68 by melting the photoresistmaterial.

In FIG. 5D, horizontal portions of the spacer layer 70 are etched(anisotropically) during the hardmask etch process. This removes spacerlayer material, if it is present, from the bottom 70 of the trench 68.This etching step also removes the hardmask material at the trenchbottom 70 to expose the base layer 62. The spacer layer verticalportions 74 that cover the trench side walls 71 are left intact duringthis process. The hardmask etch step is conventionally performed usingreactive ion etching, with a halogen or halogen compound etchant beingtypically used. This process initiates the formation of a narrowedtrench 76 that is narrowed according to approximately twice thethickness of the spacer layer vertical portions 74.

The thickness of the spacer layer vertical portions 74 may be controlledto range from zero up to about 200 nm. At that point, the time requiredto deposit additional spacer layer material may act as a disincentiveagainst further increases in spacer layer thickness. The thickness atwhich the spacer layer 70 is applied will also depend on the startingwidth of the trench 68, with less spacer layer material being requiredfor trenches of small size.

Note that if the spacer layer 72 is deposited according to the two-stepdeposition process described above, a base layer of tantalum or titanium(or other material) could be applied at a thickness of about 50 nm, andthe second layer of tungsten (if used) could be applied at a thicknessof about 0-150 nm.

In FIG. 5E, the base layer etch is conventionally performed usingreactive ion etching, with an oxidizing etchant being typically used.This process defines the narrowed trench 76, which as stated above isnarrowed according to approximately twice the thickness of the spacerlayer vertical portions 74. Moreover, because the spacer layerdeposition process produces a relatively smooth surface on the spacerlayer vertical portions 74, the narrowed trench 76 can be contoured moreprecisely than a trench formed purely lithographically.

The base layer etch process also removes the photoresist layer 66 whiletypically leaving behind all or part of the spacer layer verticalportions 74. A feature, such as a metallic pole piece, may now be formedby electroplating metallic material into the narrowed trench. Thehardmask 64, the spacer layer vertical portions 74 and the polymer layer62 may then be removed, preferably by a combination of dry and wet etchprocesses.

Accordingly, an isotropic deposition method for trench narrowing ofmagnetic write head features to be created by reactive ion etching hasbeen disclosed. While various embodiments of the invention have beendescribed, it should be apparent that many variations and alternativeembodiments could be implemented in accordance with the invention. Forexample, although fabrication of the pole tip 38 a is shown in FIGS.5A-5E, the disclosed method could also be used to fabricate the pole tip36 a, as well as the coils 32 of the combined layer 30/32 (to reducecoil pitch). It is understood, therefore, that the invention is not tobe in any way limited except in accordance with the spirit of theappended claims and their equivalents.

What is claimed is:
 1. An isotropic deposition method for trenchnarrowing of thin film magnetic write head features to be created byreactive ion etching, comprising the steps of: forming a polymeric baselayer over a substrate; applying a hardmask layer over said base layer;applying an imaging photoresist layer over said hardmask layer; defininga trench in said photoresist layer that exposes said hardmask layer,said trench having substantially vertical side walls and a bottomdefined by said hardmask layer; depositing a spacer layer isotropicallyor directionally at an angle using a deposition process to cover saidtrench side walls; performing a first anisotropic etching process toremove horizontal portions of said spacer layer and said hardmask fromsaid trench bottom while leaving intact vertical portions of said spacerlayer that cover said trench side walls, thereby initiating formation ofa first portion of a narrowed trench; and performing a secondanisotropic etching process to extend said-narrowed trench through saidbase layer to said substrate; whereby a magnetic write head feature ofreduced feature size may be formed in said narrowed trench.
 2. A methodin accordance with claim 1 wherein said spacer layer is applied using anisotropic low temperature vapor deposition or ion beam depositiontechnique and said spacer layer comprises a material that can bedeposited isotropically over said photoresist layer while preserving thegeometry of said trench.
 3. A method in accordance with claim 1 whereinsaid spacer layer is applied at an angle using a directional ion beamdeposition technique, with or without substrate rotation, and saidspacer layer comprises a material that can be deposited directionally atan angle over said photoresist layer.
 4. A method in accordance withclaim 1 wherein said first etching process uses a halogen or halogencompound etchant, said second etching process uses an oxidizing etchant,and said spacer layer comprises a material that is etchable by saidfirst etching process and resistant to said second etching process.
 5. Amethod in accordance with claim 1 wherein said spacer layer comprises ametal or a semiconductor, including carbon, or an oxide, a nitride, acarbide or other compound or alloy thereof.
 6. A method in accordancewith claim 1 wherein said spacer layer comprises a material or an oxide,a nitride, a carbide or other compound or alloy of a material selectedfrom the group consisting of silicon, germanium, tungsten, tantalum andtitanium.
 7. A method in accordance with claim 6 wherein said spacercomprises a first deposition layer of a first one of said materials anda second deposition layer of a second one of said materials.
 8. A methodin accordance with claim 7 wherein said first deposition layer comprisesa layer of tantalum or titanium that is deposited using an ion beamdeposition process, and said second deposition layer comprises a layerof tungsten that is deposited using a chemical vapor deposition process.9. A method in accordance with claim 1 wherein said spacer layer isdeposited at a thickness of up to about 200 nm.
 10. A method inaccordance with claim 9 wherein said spacer layer comprises a first ionbeam deposited layer of tantalum or titanium having a thickness of about50 nm, and a second chemical vapor deposited layer of tungsten having athickness of up to about 150 nm.